There are some exercises that you can skip, some that are good to do, and then there are some that absolutely must be in your program each week. All exercises stimulate different things in your body, some stimulate calorie burn, some impact the metabolism to a greater degree and some increase hormone production. These three stimulate all three responses, so whether you are trying to gain muscle, burn fat or just get in a little better shape you need to be doing these at a minimum once per week. And the most beautiful thing about these exercises is that you can do them almost ANYWHERE! Can't make it to the gym today? No problem, give me the time it would take to drive to the gym and back and you can still get results.

Squat - You need to do squats until you can't. If you are strong enough then add some weight. If you are really strong than add a lot of weight. Squats, assuming you have good form, increase the strength of the knee joint in all directions, use about every leg muscle that you have, increase your GH levels and stimulate a strong metabolic response. You need to do them to the point that your legs are wobbly to get the desired results, but these are incredible and really kick your butt (that is why so many people skip them).

Push-ups - Just a plain old push-up is very effective exercise. You have to use all of your pushing muscles as well as core stabilizers, leg and hip stabilizers, even your calves have to do some work! Great for burning huge calories and an almost limitless way to make them more difficult as you get better at them. They will not make you get big but they are very effective at giving that toned look, and for most you will gain some muscle.

Pull-ups - A pull-up is a fantastic way to blast your whole body. It takes lots of strength from your pulling muscles as well as good core strength. If you aren't strong enough to do a pull up yet then you can modify it down to make it easier. Use the assista-chin machine at the gym to get some added assistance, use a partner to help lift you up, or do an inverted row off of a bar. No matter what style you choose for this movement you will work all of your postural muscle, all of your core muscle, and all of your pulling muscles.

The combination of these three exercises basically hits all of your major movers, most of your assisting muscles and all of your core muscles. I am not saying that these should replace a full gym workout, but incorporating these into your program can really help you maximize the time that you have for the gym!